Instrument hardware control valves

Petrofac Training

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Instrument Hardware:Control ValvesUnit I-10

Unit I-10: Control Valves


Objectives

At the end of this unit, the trainee will be able to:

Identify types of control valves

Understand their control functions


Introduction


Components of a Control Valve


Valves can be activated using several different types of energy:

- Human

- Pneumatic Energy

- Electrical Energy

- Hydraulic Energy


The most important advantages of pneumatic control valves are:

- The construction is simple and robust.

- The power output produced by the actuator is effective and direct.

- The valve needs relatively little maintenance.


Valve Actuator

Actuators are designed so that when the controller signal output is increased to the control valve, it will either lower or raise the valve stem.


Bonnet and Gland Assembly

The middle part of a control valve is known as the Valve Bonnet.

The packing material is held in a Gland Assembly.


Valve Bonnet and Gland Assembly


Valve Body

Two most common types are:


Contoured Plug


V-Port Plug


Advantages and Disadvantages

- Flow In Contoured Plug is evenly spread over plug surface area but flow in V-Port is localized and can cause erosion problem.

- V-Port can be more easily ‘characterised’.

- V-Port is lighter than the solid contoured plug and easier to manufacture.

- V-Port accumulate dirt and sludge. The design of the contoured plug make this impossible.


Single and Double Seat Arrangements


Single Seat Contoured Plug


Double Seat Contoured Plug


Double Seated (Or Double Ported) Valve


Different Types of Valve Plugs


Fluted Valve Plug


Cage Guided Valve Plug


Hand-wheels are for manual positioning of the valve plugs:

- On failure of air supply to actuator

- During start-up

- During an emergency

- When the control valve is not provided with a bypass valve.


Control Valve with Hand-wheel


Valve Lift/Flow Characteristics


Semi throttle Characteristics‑


Main process applications of equal percentage characteristic valve

‐ Linearisation of Flow Loops

‐ Uncertain Flow Conditions


Relationship between Equal Percentage and Linear Characteristics


Special Types of Control Valves


Butterfly Valve


Ball Valve


Three Way Valve

3‐way Valve is used for flow diversion and mixing purposes.


Three Way Valve


Energised Solenoid Valve


De‐energised Solenoid Valve


Furnace Firing Control Loop


Valve Activation


Valve actions by colour coding


Robotarm Safety Shutdown Valve


Motor Operated Valves


Valve Positioners


Use of a valve positioner:

‐ When a cylinder actuator requires air pressure in excess of 15 psi

‐ When a valve is split ranged.

‐ When valves are operated in a reverse acting mode.

‐ When expected dead band of the actuator/valve combination exceeds 5% of signal span.

‐ When a booster has to be used for high stroking speed and may have excessive dead band.


Why a valve positioner should be used?

‐ To increase the speed of response in case a valve is located too far away from a control room installed I/P transducer.

Petrofac Training

Training. Competence. Excellence.

Instrument Hardware:Control ValvesUnit I‐10

Instrument hardware control valves

Engineering

Transcript of Instrument hardware control valves